1. Field of the Invention
The present invention relates to a wiring substrate having penetrating filled vias arranged in a matrix-shape.
2. Description of the Related Art
The inventors have previously invented a method of making a substrate having via conductors which penetrate the substrate. In the method large number of fine metallic wires made of copper are arranged in a container in parallel with the axis of the container. This container is filled with a dispersed solution in which ceramic powder such as alumina powder which is to be fired at high temperature is dispersed. After drying, ceramic powder is fired at high temperatures higher than the melting point of the fine metallic wires so that the ceramic powder fired at high temperatures can be sintered sufficiently densely. In this way, a columnar sintered body, which has been densely sintered, is obtained. This sintered columnar body is sliced perpendicularly to the axis, so that a substrate having via conductors which penetrate the substrate can be obtained.
According to the above method, the fine metallic wires are melted in the process of sintering the ceramic powder at a high temperatures. Therefore, even if the ceramic contracts in the process of sintering, the fine metallic wires are not broken, and it is possible to make a substrate having via conductors arranged densely in the substrate. Also, it has been confirmed by the inventors that the fine metallic wires are not diffused in the ceramic.
Further, the inventors have developed another method of making a substrate having via conductors which penetrate the substrate. In the method a large number of fine metallic wires made of copper are arranged in a container in parallel with the axis of the container. This container is filled with ceramic powder which is to be fired at low temperatures and the primary component of the ceramic powder is glass. The ceramic powder is fired at a temperatures lower than the melting point of the fine metallic wires. In this way, a columnar sintered body is obtained. This sintered body is sliced perpendicularly to the axis, so that a substrate having via conductors which penetrate the substrate can be obtained.
According to the above method, ceramic powder, which is to be fired at low temperatures and the primary component of which is glass, is melted in the process of sintering. Accordingly, stress is not applied to the fine metallic wires. Therefore, it is possible to make a substrate having via conductors which are not broken.
However, according to the former method, the following problems may be encountered. Since the ceramic fired at a high temperature contracts with a coefficient of contraction of about 40%, the dimensional accuracy is low. Further, since the ceramic is densely fired, the hardness of the ceramics is very high. Therefore, it is difficult to slice the sintered body. If any additive is added to the ceramics so as to lower the hardness, the mechanical strength would also be lowered.
According to the latter method, the following problems may be encountered. In the latter method, a ceramic fired at a low temperatures, the primary component of which is glass, is used. Accordingly, the fired ceramic is fragile, and the mechanical strength is low.